Who isn't, you say? Hardly any "ism" these days has much of a scholarly following. Yet presentism besets us in two different ways: (1) the tendency to interpret the past in presentist terms; and (2) the shift of general historical interest toward the contemporary period and away from the more distant past. Although the first propensity was implicit in Western historical writing from its beginnings, it took a more problematic turn when the notion of "the modern" began to take root in the 17th century. Over time, modernity became the standard of judgment against which most of the past, even the Western past, could be found wanting. The second trend, the shift of interest toward the contemporary period, clearly has a connection to the invention of modernity, but it did not follow as much in lockstep as might be expected. As late as the end of the 19th century, and in some places even after that, students in history expected to study mainly ancient history and to find therein exemplars for politics in the present. Ten or fifteen years ago, survey courses routinely stopped at World War II. French historians still refer to history in the 16th–18th centuries as histoire moderne; for them "contemporary history" began in 1789, and until recently, it stopped about the time of World War I, the rest of the 20th century being consigned to the province of journalism rather than historical scholarship. I believe that the 20th century should be part of historical scholarship and teaching, of course, but it should not crowd out everything else.
There is a certain irony in the presentism of our current historical understanding: it threatens to put us out of business as historians. If the undergraduates flock to 20th-century courses and even PhD students take degrees mostly in 20th-century topics, then history risks turning into a kind of general social studies subject (as it is in K–12). It becomes the short-term history of various kinds of identity politics defined by present concerns and might therefore be better approached via sociology, political science, or ethnic studies. I'm not arguing that identity politics have no place in historical study; women's history, African American history, Latino history, gay and lesbian history, and the like have all made fundamentally important contributions to our understanding of history. It is hard to imagine American history in this country without some element of national identity in it. And present-day concerns have helped revivify topics, such as imperialism, that needed reconsideration. But history should not just be the study of sameness, based on the search for our individual or collective roots of identity. It should also be about difference. World history, for example, should be significant not only because so many Americans have come from places other than European countries but also because as participants in the world we need to understand people who are hardly like us at all.